1. Field of the Invention
The present invention relates to a lens supporting mechanism in a lens barrel in a video camera or the like.
2. Description of the Related Art
There is a method of supporting a lens barrel in which a lens retaining frame is supported in a space with a thin shaft called “rod” or “guide bar” (for example, see Patent Document 1). There is also another method of supporting a lens barrel in the related art in which the lens retaining frame is supported in a space using three pins (cam followers) and cam grooves (for example, see Patent Document 2).
As described in a first embodiment of the lens barrel (pp. 3, FIGS. 1, 2 and 3), there is a video lens barrel in which a lens retaining frame (movable lens frames 5 and 6) is supported with two guide bars 3 and 4) fixed at both ends to a fixed barrel 1 and a fixed barrel 2 so as to be capable of moving in the direction of optical axis. Zooming is performed by driving the first movable lens frame 5 by a first stepping motor 11, and driving the second movable lens frame 6 by a second stepping motor 12.
As described in the first embodiment of an optical apparatus, a general lens barrel using a cam includes three follower pins 1-a provided outside a moving first frame group 1 are fitted respectively into an elongated hole 4-a on a straight barrel 4 and a cam groove 5-a of a cam cylinder 5 (see FIG. 5 in Japanese Patent Application Laid-Open No. H07-120656). Likewise, three follower pins 2-a provided outside a second frame group 2 are fitted respectively into the elongated hole 4-a on the straight barrel 4 and a cam groove 5-b of the cam barrel 4 (see FIG. 5 in Japanese Patent Application Laid-Open No. H06-174998). When a zooming and focusing motor 8 is driven, the cam barrel 4 rotates, and hence the first frame group 1 and the second frame group 2 are driven in the direction of the optical axis (pp. 3, FIG. 1, FIG. 4, and FIG. 5).
The lens barrel of a guide-bar type in the related art described above has following characteristics. (1) Since the guide bar is fixed at both ends to the fixed barrel or the like, it has a fixed beam structure, the midsection of the guide bar may be bent, and hence accuracy of eccentricity of the lens retaining frame is deteriorated, whereby quality of picture image may be deteriorated. (2) The guide bar, which is a single component, is required to have high degree of accuracy in its diameter or straightness, whereby the manufacturing cost is high, and thus the cost of the lens barrel may be increased. (3) The lens retaining frame is required to have a sufficient thickness for surrounding the guide bars to be fitted, whereby the lens barrel may be upsized.
The lens barrel of a cam pin type in the related art as described above is characterized by its multifunction and compact design since the lens retaining frame is retained in the lens barrel and is driven only by three cam pins disposed outside the lens retaining frame. However, such multifunction may cause deterioration of the level of accuracy in eccentricity, which is difficult to improve.